As a consequence of the success of the DS-2A Tom decided to produce a small analog synthesizer module to be used in conjunction with the sequencer. It was designed so that it could also be used to enhance the sound possibilities of the ARP & Moog products by means of its multi-mode filter. The Synthesizer Expander Module is a complete, classic analog synthesizer implemented with two precision voltage controlled oscillators (VCOs), a wide-range 2-pole multi-mode filter (VCF), two envelope generators and a low frequency oscillator (LFO). Included within the module design are selectable modulation sources for modulating the VCOs and the VCF. Internal connections can be applied to panel jacks in to allow integration of the module with external equipment.